I wish it had been an unseated cable. Today, I tried the old drive again, and the 8300 repeated the same symptoms, except it did finally reboot instead of looping. After booting, it did not show any increase in disk capacity, so it was not reading the drive.
The drive still works though. Initially, I couldn't read it with Vista. XP, or Linux. I just repartitioned it with NFTS and a Linux (etc2) partitions, and it now passes diagnostics and is readable on either Windows or Linux. Go figure. Maybe it got glitched somehow in a critical spot or the kids bumped it while messing around with their WII console.